1. Field of the Invention
The present invention relates to a ceramic vertebrae prosthesis which utilized as a substitute for one or more intervertebral disks that have been resected in a resection operation.
2. Description of the Related Art
If a nerve root is subject to a pressure due to an injury of an intervertebral disk, such as a cervical vertebrae, various neurological symptoms often arise therefrom. To cure this problem, the injured portion is usually subject to local rest and fixation thereof and a conservative curing process, such as an extensive curing process. Notwithstanding, if pain is not remitted, or the injury is too severe to be restored by such a curing procedure, a patient undergoes a surgical operation. There are two surgical operation methods in which the injured intervertebral disk is removed in front of the body of the vertebra or the vertebral arch is partly resected in the rear of the body of the vertebra so as to deliver a hernia. The first operation method in which the injured intervertebral disk is resected in front of the body of the vertebra is referred to as a forward adhesion in which a bone is implanted and adhered in a cavity formed between the upper and lower bodies of vertebra.
In such a forward adhesion, in many cases, a self-iliac bone is used as a bone to be implanted. However, a patient suffers from heavy burden and physical load as a result of to a secondary invasive procedure necessitates by the extraction of the iliac bone. To this end, prostheses, such as ceramics have been recently used and implanted instead of the self-iliac bone. In general, the ceramics are stable in and highly biocompatible, with the organ in which the prosthesis is to be grafted.
However, the ceramics are brittle and hard, and accordingly are weak with respect to physical shock. It is necessary for a vertebra prosthesis to have a mechanical strength strong enough to resist the compression load exerted to upper and lower vertebra bodies. In addition thereto, the vertebra prosthesis must be brought into direct contact with or directly adhered to the bone without an intervening soft tissue between the prosthesis and the bone while no bone resorption occurs between the upper and lower vertebra bodies.
The shape of the prosthesis is such that the portion of the bone to be resected is as small as possible, since the prosthesis must be partly removed in accordance with the shape of the vertebrae prosthesis. In general, a known prosthesis (prosthesis other than ceramics) is subject to a certain stress (pressure) due to repeated absorption and bone resorption with respect to a sound bone to keep a balanced state. However in particular, the ceramic cervical vertebrae prosthesis in which no bone resorption takes place must be shaped so as to disperse or uniformly distributes the compression stress. Nevertheless, the conventional ceramic vertebrae prosthesis has been focused mainly on the strength of the material of which the vertebrae prosthesis is made, to increase the resistance to the compression load but little or no consideration of the shape have been taken into account. Moreover, little or no attempts to reduce the amount of the bone to be resected have been made.
Furthermore, it is necessary to expand the distance between the upper and lower vertebra bodies so as to insert the vertebrae prosthesis therebetween. However, the conventional vertebrae prosthesis cannot, by itself, expand the distance between the upper and lower vertebra bodies. Accordingly, it is necessary to use a special expanding tool or device, thus resulting in an increase in the time for the operation. In particular, a conventional elongated prosthesis, which is to be inserted to substitute for a plurality of removed vertebra bodies, is usually in the form of a circular or angular post linearly extending in the vertical direction. Accordingly, it does not conform to the profile of the continuously curved vertebra bodies. Consequently, the conventional elongated prostheses were morphologically unnatural.